5.1 SoilIB Environmental Systems and Societies HL: Subtopic test

1. 1
   A soil pit is dug in an old broadleaf woodland in southern England. At the surface is a thin layer of leaf litter and partly decomposed material. Below it is a dark, crumbly layer full of roots, humus and soil organisms. Beneath that is a paler layer made mostly of weathered mineral material with little organic matter. At the base, large fragments of unweathered chalk lie in the loosened bedrock.

   (a)

   The dark layer rich in humus and roots just beneath the litter is best identified as which horizon?

   [1 mark]

   • AO horizon
   • BB horizon
   • CA horizon
   • DC horizon

   (b)

   The layer of broken, weathered chalk at the base of the pit is the:

   [1 mark]

   • AC horizon (parent rock)
   • BA horizon
   • CO horizon
   • DB horizon

   (c)

   Explain why the A horizon is the most valuable layer for plant growth but is also vulnerable.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A prairie in central North America has never been ploughed. Its soil holds the seeds of many species of grass and wildflower, stores rainwater through the dry summer, and supports huge numbers of bacteria, fungi, earthworms and burrowing mammals. Dead roots and leaves decompose and release nutrients that the grasses absorb again.

   (a)

   Which of the following is NOT normally obtained by plants from the soil?

   [1 mark]

   • AWater
   • BNitrogen compounds
   • CPhosphorus compounds
   • DCarbon

   (b)

   The reuse of nutrients released by decomposition in the prairie is an example of the role of soil in:

   [1 mark]

   • APrimary production
   • BRecycling elements as part of biogeochemical cycles
   • CProducing a seed bank
   • DHeat loss from the ecosystem

   (c)

   Outline two ways in which the prairie soil contributes to biodiversity.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student analysed two soils. Soil 1: 60% sand, 25% silt, 15% clay; organic matter 2%; water content 8%; infiltration rate 60 mm per hour; bulk density 1.5 g cm⁻³; pH 5.0. Soil 2: 25% sand, 30% silt, 45% clay; organic matter 6%; water content 28%; infiltration rate 4 mm per hour; bulk density 1.1 g cm⁻³; pH 7.0.

   (a)

   Calculate how many times greater the infiltration rate of Soil 1 is than that of Soil 2, and explain the difference in terms of the particles in the soils.

   [3 marks]

   (b)

   Using the data, evaluate which soil is likely to support higher primary productivity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hillside beech woodland on chalk in southern England is to be cleared and planted with vines. At present the woodland has a thick litter layer over a deep dark A horizon. A soil scientist warns that clearing the woodland could turn the soil from a carbon store into a source and that the topsoil could be lost from the slope.

   (a)

   Explain how clearing the woodland could change the carbon balance of the soil and the inputs and outputs of the soil system.

   [6 marks]

   (b)

   Explain how the factors that influence soil formation produced this woodland soil, and why the A horizon needs careful management if the land is converted.

   [6 marks]

   Total for question 4: 12 marks

End of questions